In the field of fiber optical communication, there are many important applications where it is necessary to align, with high precision, an optical fiber with an electro-optical device such as a semiconductor light emitting device or a semiconductor photodetector device.
A type of semiconductor light emitting device which is useful for application in the invention is a so-called tilted-charge light-emitting device (TCLED). These devices include three terminal light-emitting transistors (LETs), three terminal transistor lasers (TLs), and two terminal tilted charge light-emitting diodes. Reference can be made to the following documents: U.S. Pat. Nos. 7,091,082, 7,286,583, 7,354,780, 7,535,034, 7,693,195, 7,696,536, 7,711,015, 7,813,396, 7,888,199, 7,888,625, 7,953,133, 7,998,807, 8,005,124, 8,179,937, and 8,179,939; U.S. Patent Application Publication Numbers US2005/0040432, US2005/0054172, US2008/0240173, US2009/0134939, US2010/0034228, US2010/0202483, US2010/0202484, US2010/0272140, US2010/0289427, US2011/0150487, and US2012/0068151; and PCT International Patent Publication Numbers WO/2005/020287 and WO/2006/093883, and the publications referenced in U.S. Patent Application Publication Number US2012/0068151.
In a typical optical transmitter assembly, a chip containing a semiconductor light emitter is coupled with a fiber optical cable, the proximal end of which is mounted in a connector. The chip is secured to a printed circuit board. The semiconductor light emitter may have an associated lens for focusing emitting light into the optical fiber.
The efficient coupling of light from the light-emitting device, with or without a lens, into an optical fiber, is an important aspect of fiber optical communication. Efficient coupling requires precise alignment of the optical axis of light from the light-emitting device with the axis of the input end of the optical fiber. If there is misalignment, a substantial portion of the light may be lost, resulting in undesirable attenuation of the optical signal. Accordingly, precise alignment is recognized as being an important part of producing an optical transmitting assembly.
FIG. 1 is a diagram illustrating an active alignment procedure as utilized in the prior art. [See “Nanometric Positioning Technology”, CVI Melles Griot, http://www.cvimellesgriot.com/products/Documents/TechnicalGuide/Nanometric_Positioning_Techlnology.pdf]. In the diagram of FIG. 1 there is shown a focused laser light source 110, a focusing lens 115 and an optical fiber 120. Also shown are the optical axis x, the lateral axis y, and the vertical axis z. When coupling the light from the focused laser source into the optical fiber 120, aligning the fiber to the lens requires a minimum alignment with three axes X, Y and Z. Depending on the manufacturing and fixturing tolerances of the components, adjustment in roll (theta x), pitch (theta y) and yaw (theta z) may be needed.
U.S. Pat. No. 7,068,891 discloses a system and method for aligning and positioning optical fibers, including a system and method for actively aligning an optical fiber to a laser diode. The '891 patent references U.S. Pat. No. 4,694,477, which discloses an apparatus having six degrees of freedom. A single first stage is supported vertically by three actuator assemblies. The actuator assemblies consist of a number of flexures respectively coupling piezoelectric transducers to the first stage at three equiangular points. In the '477 patent, the three vertical actuator assemblies accomplish vertical linear motion and rotation about two perpendicular horizontal axes. Three similar horizontal actuator assemblies are attached to the first stage for accomplishing linear movement of first stage along two perpendicular horizontal axes. When the two parallel horizontal actuator assemblies are moved in opposite directions, rotation of the first stage about the vertical axis is accomplished. Each of the pivot points for the pitch, roll and yaw motions is located within the stage assembly. The '891 patent indicates that this limits the range of travel of the '477 patent equipment. The '891 patent discloses an instrument and method for positioning an article with six degrees of freedom about a selectable pivot point. The instrument includes a base stage for linear motion in two perpendicular axes wherein the perpendicular axes form a plane. A yaw stage is coupled to the base stage for rotational motion about a third axis normal to the plane. The yaw stage has a pivot point locatable outside an envelope defined by the yaw stage. A three-axis stage coupled to the yaw stage provides for rotational motion about each of the two perpendicular axes and linear motion along the third axis. The third stage may also include a mount for fixing the article thereto. A control system is in communication with each of the stages for controlling the positions thereof.
The complexity of the alignment systems and techniques of the prior art, such as in the '477 and '891 patents, is particularly striking. In addition to requiring complex and expensive equipments, typical prior art alignment techniques are complicated and time consuming, and therefore tend to increase the cost of opto-electronic equipment.
It is among the objectives of the present invention to address the indicated limitations of prior art apparatus and techniques and to provide improved alignment of opto-electronic components.